1. Field of the Invention
The present invention relates to an electrostatic painting device, and more specifically to an electrostatic painting device wherein a spray distance of an electrostatic spray gun relative to an article to be coated may be maintained so as to provide a good efficiency of spray coating.
2. Description of Related Art
An electrostatic painting device is so designed that particles of painting material which have been atomized are electrically charged and the thus atomized particles of painting material are electrostatically adhered on the article to be coated by using the electrostatic field formed between electrodes at an outlet of the electrostatic painting device and the article to be coated. An electrostatic painting method is highly appraised and widely utilized in view of excellent coating efficiency, enhanced productivity and protection against environmental pollution. As described in Japanese Patent Disclosure Publication No. Heisei 10-128170 which was disclosed on May 19, 1998, an electrostatic spray gun of internal pressure boosting type which incorporates a high voltage boosting circuit has been developed as an electrostatic painting machine. In order to allow the particles of painting material to be electrostatically adhered efficiently on the article to be painted, it is necessary to keep the spray distance of the electrostatic spray gun relative to the article to be coated within a specific proper range. Should the spray distance of the electrostatic spray gun relative to the article to be coated be too short (or should the electrostatic spray gun be placed too near to the article to be coated), a surface to be coated will get too coarse to obtain a good coated surface. On the contrary, should the spray distance be too far apart (or should the electrostatic spray gun be placed too far from the article to be coated), the effect of the electrostatic field will be degraded, resulting in an inability to maintain a good coating efficiency.
When carrying out coating work quickly without considering the maintaining of a high level of coating efficiency, the coating work may be performed more easily if the discharge amount of the painting material is increased and the spray distance is kept longer. On the other hand, when carrying out the spray coating work even though the discharge amount is not particularly increased but the spray distance is kept rather longer, formation of the film on the surface to be coated is performed without specific problems despite the coating efficiency and the speed of the coating work being rather decreased. Besides, by doing so, it is not necessary to pay too much attention to keeping the distance between the spraying gun and the article to be coated within an optimum range of distance. Since it is possible to execute coating even though the electrostatic spray gun is held somewhat roughly, there is a tendency for the coating workers to unconsciously keep the spray distance rather longer.
In the meantime, if the spray distance is kept shorter, or the spraying gun is brought nearer to the article relative to the optimum spray distance, the surface to be coated may become rather coarse, resulting in the need to re-spray the coating. Furthermore, if the spray distance is too short, over-load electric current will be caused to flow through the electrostatic spray gun, and a control may sense this over-load current to provide an abnormal indication or suspend high voltage charging and spraying of the painting material on the safe side. Under these circumstances, a worker tends to unconsciously keep the spray distance longer rather than shorter.
According to the conventional electrostatic painting machine, since no measures were taken for detection devices or the like to detect if the spray distance is longer than the specified proper distance, keeping the spray distance within a proper range depended on the vigilance of the workers. More recently, however, as the issue of global environmental pollution prevention becomes increasingly more important, so too does the need to maximize the coating efficiency and limit the environmental air pollution due to wasteful spraying of painting material. For example, if the normal to optimum spraying distance of 200-250 mm is increased to 300 mm, the spray coating efficiency may be decreased by a few percent, although this depends on the shape of the article to be coated and the kind of the painting material to be used.
An object of the present invention is to provide an improved electrostatic painting device wherein coating work may be performed while keeping the spray distance of the electrostatic spray machine, relative to the article to be coated, within an optimum distance range, thereby optimizing coating efficiency and preventing the workers from unconsciously extending the spray distance out of the optimum distance range.
Another object of the present invention is to provide an electrostatic painting device wherein in the case that the spray distance is longer than the optimum distance range, intensity indication may be proportional to the length of the spray distance.
In order to attain the objects as above mentioned, the electrostatic painting device according to the present invention comprises an electrostatic painting machine provided with a high voltage generation part adapted to supply high voltage to the atomized painting material, detection means adapted to detect load current which varies depending on the spray distance between the painting machine and the article to be coated processing means having a threshold corresponding to the maximum distance within the optimum spray distance range and adapted to output an alarm signal when the detected load current falls below the threshold and alarming means adapted to receive the alarm signal and provide an alarm indication.
According to an embodiment of the present invention, the processing means is adapted to output an alarm signal in proportion to the difference between the threshold and the detected load current when the detected load current falls below the threshold while the alarming means is adapted to provide the alarm indication of the intensity corresponding to the alarm signal. Thereby, the approximate length of the spray distance between the information regarding the electrostatic painting machine and the article to be coated may be provided to the coating workers. According to a further embodiment of the present invention, the threshold corresponding to the maximum distance may be set by adjusting it separately for each electrostatic painting machine based on the relationship between the spray distance of the electrostatic painting machine and the load current.